The invention relates to an arrangement for the dosed injection of a reducing agent into the exhaust tract of an internal combustion engine, particularly of a diesel engine, using for example a piston pump for the pulsed delivery of the reducing agent to a nozzle extending into the exhaust tract of the engine.
It is known to reduce the nitrogen oxide in the exhaust gas of internal combustion engines, particularly diesel engines, by selective catalytic reduction. To this end, an aqueous urea solution is injected into the exhaust tract finely atomized and in a dosed manner. For pressurizing the reducing agent generally a pump is used which supplies the reduction agent to a nozzle via which the reduction agent is injected into the exhaust tract.
US 2004/0093856 A1 discloses a dosing arrangement for reducing agents, which utilizes a piston pump. The pump includes a suction connection, which is in communication with a storage container for the reducing agent, and a pressure connection which is in communication with an atomizing device. The atomizing device extends into the exhaust tract of an internal combustion engine in the area of a Denox catalytic converter. For controlling the supply volume, the frequency or the pulse width is varied. To this end, a control device is used which, dependent on the engine operation, adjusts the energizing current for the pump in a suitable manner. The design of the nozzle is not shown. But it is assumed that the nozzle includes, as is common, one or several openings which are always open. With such a nozzle, a uniform atomization over the whole operating range cannot be achieved with varying injection volumes.
EP 1 380 733 A2 discloses a piston pump for the dosing of aqueous urea solutions including a piston which is operated by a piezo element. The piezo element can be operated at a frequency of from 0 to several hundred Hertz by stepless control. The nozzle for the injection of the reducing agent into the exhaust gas tract of an internal combustion engine apparently includes a diaphragm-like restriction which is always open. A uniform atomization over the whole operating range cannot be achieved with such a nozzle if the injection volume changes.
Another device for dosing the reducing agent injection into the exhaust tract of an internal combustion engine is known from DE 101 39 139 A1. A pump is used therein to pump the reducing agent by controlling an electric pump drive. The control unit also controls the operation of a dosing valve integrated into a dosing arrangement. It is further said that, in place of a dosing pump, a simple pump in connection with a pressure control valve could be used for controlling the admission volume. Also in this variant, the dosing of the injection amount obviously occurs by means of a dosing valve. The arrangement appears to be expensive since the pumping and the dosing involves different components which need to be controlled separately.
DE 22 49 291 discloses a method for airless paint spraying which however should be of no importance in considering the inventive level of the present invention since such a device is not concerned with a related field. Nevertheless, in this publication, a pulsing membrane pump is used for supplying paint to an atomizing nozzle, which is in the form of a blocking valve similar to an over-pressure valve. The blocking valve automatically opens and closes periodically in such a way that during a pressurizing period the paint supply is interrupted in the low pressure range, so that atomization occurs exclusively in the high-pressure range. Herein, only the pressure peaks are utilized for the atomization which provide for the finest atomization.
It is the object of the present invention to provide an arrangement for the injection of a reducing agent into the exhaust tract of an internal combustion engine with a high atomizing quality independently of pumping or injection volume using simple and inexpensive equipment.